Project Summary/Abstract Multidrug resistant (MDR) Gram-negative bacteria represent a global health crisis. Traditional antibiotics create selective pressure and breed resistance, making our current drugs less and less effective. Targeting of bacterial virulence factors has gained interest as an alternative strategy to potentially circumvent this problem. Virulent Acinetobacter baumannii rely on multiple virulence mechanisms to establish infection, including biofilm formation and siderophore-mediated iron acquisition. Biofilms are communities of bacteria bound together by extracellular matrices that adhere to surfaces and display enhanced antibiotic resistance, and siderophores are small- molecule chelators that scavenge life sustaining iron from host sources. Recently, a group of natural products dubbed the cahuitamycins were structurally characterized and determined to have biofilm-inhibitory activity against A. baumannii. The cahuitamycins contain bidentate chelating motifs found ubiquitously in siderophore structures (phenolate-oxazoline and hydroxamate); however, ring-opening of the oxazoline completely abolishes anti-biofilm activity. This heavily implies that the siderophore-like nature of these molecules is closely related to their mechanism of antibiotic activity. Herein, we propose to study the cahuitamycins to shed light on the biochemical connection between these two clinically relevant virulence factors. To this end, we propose two interrelated aims focusing respectively on the organic synthesis of cahuitamycins and analogs thereof, and on the biological evaluation of the cahuitamycins and the siderophore-biofilm relationship in A. baumannii. We have devised a synthetic route to the cahuitamycins that is highly convergent for the rapid generation of diverse analog panels. Derivatives will be tested for their ability to inhibit biofilm-formation, and the resulting structure- activity relationships will be used to design functionalized cahuitamycin probe molecules. In parallel, biofilm formation in A. baumannii will be evaluated using siderophore-deficient mutant libraries, phenotypic profiling by confocal microscopy, and transcriptomic analysis of cahuitamycin-treated A. baumannii. Use of Activity-based Protein Profiling will enable cahuitamycin target identification, and computational docking will provide insight into mechanism of action. This proposal integrates two cutting edge research areas in the field of infectious disease, biofilm formation and siderophores, and as such is positioned to produce highly impactful and foundational work for the future development of novel anti-virulence therapeutics.